The objective of this study is to characterize regional hemodynamics in an experimental model of early left ventricular failure (LVF) in which left artrial pressure (LAP) is elevated by supravalvular aortic constriction. Eight pilot experiments, performed in chronically instrumented calves, prove that the objective is feasible because the model is stable. Other attempts to produce LVF (by coronary artery occlusion or embolization, by production of mitral valve incompetence or stenosis, by shunting blood from the aorta to left atrium in combination with aortic constriction, or by abdominal aortic constriction alone) have been subject to ventricular fibrillation, pulmonary edema or severe depression of cardiac output (CO) which render all of them unstable. Because acute elevation of LAP causes total systemic resistance to fall, it may also fall in this model. In acute preparations skin, muscle, intestine and renal vascular beds dilate when LAP is elevated. In contrast, constriction of these beds occurs with congestive heart failure when CO is decreased. Characterization of the hemodynamics of these beds in this model will provide an opportunity to extend the observations on flow distribution to intact, unanesthetized animals. And, the model will provide a preparation in which to demonstrate the ability of a left ventricular assist device to restore normal flow distribution. Pumps of this type are preload sensitive and are unable to pump more than 1/3 to 1/2 of the cardiac output when they fill at normal left atrial pressure. Four series of experiments will be done in calves which will serve as their own controls prior to each experimental intervention. Blood flow will be measured by implanted electromagnetic flow probes, and catheters will be implanted for pressure and flow measurements and infusions. Aortic constriction will be performed with an implanted hydraulic occluder. Exercise and pulmonary stenosis will be added to the rest and LVF conditions with and without physical and pharmacologic interruption of the reflexes initiated from atrial and ventricular pressure receptors. Data will be analyzed daily.